Image Math CAPTCHA For Drupal
This module is an add-on for the CAPTCHA module to provide a mathematical equation challenge as a CAPTCHA. The question presented is an image instead of text to prevent auto-crawling and parsing via robots. Images are created on the fly much like the Image CAPTCHA module that comes with CAPTCHA.
This module used Image CAPTCHA as a foundation and was modified from that. So all due credit to the creators of CAPTCHA for providing that starting point